The invention relates to implantable medical devices having rechargeable thin-film microbattery power sources.
Current implantable medical devices require an electrical power source that contains one or more volatile components. These volatile components must be effectively contained in the battery throughout the life of the medical device. Typically, the volatile component is a liquid electrolyte. However, it may also be a cathode material as in the lithium/iodine battery, or a combined electrolyte/cathode (xe2x80x9ccatholytexe2x80x9d), as in a lithium/thionyl chloride battery. In any case, leakage of these materials will cause catastrophic failure of the circuit or electronics of the device.
Typically, the volatile components are contained by housing the active battery materials in a corrosion resistant metal case. The metal case is usually hermetically sealed either through a crimped seal with a polymer gasket, or by a welded seal. In the latter case, at least one electrical feedthrough (also hermetic) is required to access one electrode of the battery. The second electrode is often accessed by contact with the hermetic, metallic enclosure of the battery. The feedthrough is a relatively expensive component, requires extensive internal insulation, and is volumetrically inefficient.
Both crimped-seal battery enclosures and welded battery enclosures require verification of hermetic seal integrity. With a crimped-seal battery, this is typically accomplished by storing the battery for a period of approximately 30 to 45 days, and then visually inspecting for signs of leakage (i.e., salt crystal formation or corrosion). This is a highly undesirable process due to the long manufacturing cycle time and the large delay between the initiation and detection of any issue with seal integrity. In addition to the need for and difficulty in verifying the integrity of the seal, crimped-seal batteries typically require a circular shape that is difficult to package efficiently in an implantable medical device because of unused space at the xe2x80x9ccornersxe2x80x9d when the circular shaped device is placed in the medical device and adjacent to the substrate circuit board upon which the electronics are located.
Welded-seal batteries are typically subjected to a leak test procedure prior to filling with electrolyte, and then tested again after the final seal is welded in place. The first leak check is accomplished by pulling a vacuum on the welded battery case and cover through the electrolyte fill port while spraying helium on the exterior of the case. If helium leaks into the interior of the case, it is detected by a mass spectrometer. The second (final) leak check is more complicated. After the battery is filled with electrolyte (or cathode or catholyte) through a specially designed fill port, a temporary plug-type seal is placed deep in the fill port. The area above the temporary seal is either void volume or filled with a material that can absorb helium (e.g., very small porous glass spheres). A final seal is then welded in place at the entrance to the fill port, leaving a void volume or the helium absorbing material between the temporary seal and the final seal. The sealed battery is then placed in a helium atmosphere at a specified pressure for a specified time. If the final seal is not hermetic, helium will leak into the space between the two seals. The battery is then placed in an enclosure and a vacuum is pulled on the enclosure. If the final seal is not adequate, helium will leak from the fill port into the enclosure and be detected as described earlier.
Furthermore, liquid electrolyte batteries, have several added disadvantages that typically include the following: (1) a porous cathode filled with liquid electrolyte (which is volumetrically inefficient); (2) a porous or ion-conductive separator of sufficient dimension to prevent shorting by foreign particles (typically two layers of 0.001xe2x80x3 or greater); (3) a large headspace for additional liquid electrolyte (porous cathodes often swell during discharge and require additional electrolyte to ensure that they remain immersed in liquid electrolyte); (4) a large headspace to allow for appropriate electrical insulation to provide isolation of positive and negative terminals of the battery and to provide thermal insulation to prevent damage to the active components during welding of the battery enclosure, which is typical for liquid electrolyte batteries; and (5) conductive diluents to make the cathode material electrically conductive and binders to hold cathode material together, which comprise about 10% to 15% by weight of the cathode.
Crimped-seal and welded-seal batteries have several limitations with respect to geometry and physical dimensions. For example, crimped-seal designs are typically limited to circular shapes (a thin disk or cylinder). These shapes do not package efficiently in implantable devices and tend to result in a large amount of unusable volume. It also becomes very difficult to attain an adequate seal as the dimension of the seal area increases. Hence, it is difficult to build a thin, disk-shaped battery with a large diameter. Thin, large surface-area welded-seal batteries are also difficult to manufacture. Thinness is often limited by feedthrough dimensions, and surface area is limited by electrode handling properties and/or the tolerances of the case and cover materials.
Welded-seal rechargeable batteries are typically prismatic, i.e., they are rectangular prism shaped batteries with 90 degree corners. A problem with such batteries is that they do not have a curved shape, which is desirable in an implantable medical device (except for the disadvantage of unused space as previously described above for circular shaped batteries when placed adjacent to a substrate circuit board within the device).
An example of a conventional implantable medical device having a prismatic battery having a liquid electrolyte is shown in FIGS. 1A and 1B. Referring to the drawings, FIG. 1A is a top cut-away view of a conventional implantable medical device 10. Device 10 has a rechargeable battery 12 that is placed in a hermetic case 14. Device 10 also has electronics 16. Hermetic case 14 protects the electronics 16 from the liquid electrolyte (not shown) in rechargeable battery 12. Device 10 also has a connector block 18 that is used to provide an electrical connection between device 10 and electrodes (not shown), which provide electrical stimulation to patient tissue. Device 10 has a shield 20 and a cover (not shown). As shown, battery 12 has straight sides 22. Separator 24 is used to provide a physical barrier that is needed between the anode and the cathode (not shown) in battery 12 since it has a liquid electrolyte. Electronics 16 are located on a substrate circuit board 26. Device 10 also has a coil of wire for charging the battery 12 via induction. The coil (not shown), can be located either internal or external to device 10. FIG. 1B is a cross-sectional view of the conventional implantable medical device 10 taken along line Bxe2x80x94B in FIG. 1A.
An example of a conventional implantable medical device having a circular battery with a liquid electrolyte is shown in FIGS. 1C and 1D. Referring to the drawings, FIG. 1C is a top cut-away view of a conventional implantable medical device 10. Device 10 has a rechargeable circular battery 28 that is placed in a hermetic case 14. Device 10 also has electronics 16. Hermetic case 14 protects the electronics 16 from the liquid electrolyte (not shown) in rechargeable battery 28. Device 10 also has a connector block 18 that is used to provide an electrical connection between device 10 and electrodes (not shown), which provide electrical stimulation to patient tissue. Device 10 has a shield 20 and a cover (not shown). As shown, battery 28 has a continuous curved side 30. Separator 34 is used to provide a physical barrier that is needed between the anode and the cathode (not shown) in battery 28 since it has a liquid electrolyte. As shown in FIG. 1C, unused space 32 exists because the battery 28 having a circular side 30 does not fill reach the unused space 32 defined by the battery 28, shield 20 and substrate circuit board 26. Unused space 32 is one of the important disadvantages in this conventional device. Electronics 16 are located on a substrate circuit board 26. Device 10 also has a coil of wire for charging the battery 28 via induction. The coil (not shown), can be located either internal or external to device 10. FIG. 1D is a cross-sectional view of the conventional implantable medical device 10 taken along line Dxe2x80x94D in FIG. 1C.
The present invention is an implantable medical device comprising an outer housing, electronics within the outer housing, the electronics located in on a substrate circuit board, and a rechargeable thin-film microbattery within the outer housing. The rechargeable thin-film microbattery of the present invention is a solid-state battery that is devoid of liquids or other volatile materials from which the electronics must be protected.
In a preferred embodiment, the rechargeable thin-film microbattery has a straight first side that is adjacent to the substrate circuit board, and a curved second side that is adjacent to the outer housing.
In a preferred embodiment, the rechargeable thin-film microbattery lies in a plane that is parallel to the substrate circuit board containing the electronics. In a preferred embodiment, the electronics are on a top side or first face of the substrate circuit board, and the rechargeable thin-film microbattery is positioned underneath a bottom side or second face of the substrate circuit board, the second face being on the side of the substrate circuit board opposite the first face. In a further preferred embodiment, the rechargeable thin-film microbattery is deposited on the bottom side of the substrate circuit board.
In another preferred embodiment, the rechargeable thin-film microbattery lies in a plan that is parallel to the substrate circuit board and the device includes a back-up battery adjacent to the circuit board and the rechargeable thin-film microbattery.
In an alternative preferred embodiment, a first group of the electronics is located on a first face of the substrate circuit board, and a second group of electronics is located on a second face of the electronics are located on the bottom side of the substrate circuit board, and the rechargeable thin-film microbattery is located underneath or over a back-up battery, and both batteries are located adjacent to the substrate circuit board.
In an alternative preferred embodiment, the rechargeable thin-film microbattery lies in a plane that is parallel to the substrate circuit board, the electronics are located on the a first face or the first face and the second face of the substrate circuit board, and the microbattery is positioned adjacent the second face of the substrate circuit board and is adjacent to at least a portion of a back-up battery that is adjacent to the substrate circuit board.